Radio communication system and method having a radio link control layer

ABSTRACT

Disclosed are a radio link control (RLC) entity and a data processing method for the RLC entity. The RLC entity includes a transmission data storing module that stores PDUs corresponding to SDUs transmitted from a first upper layer and outputs the stored PDUs by SDU units, a ciphering module that ciphers the PDUs stored in the transmission data storing module and transmitting the ciphered PDUs to a first RLC entity, a deciphering module that deciphers the ciphered PDUs transmitted from a second RLC entity, and a received data storing module that stores the deciphered PDUs and outputs the PDUs toward a second upper layer in the form of SDU units.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.11/559,863, filed Nov. 14, 2006, which is a divisional of U.S.application Ser. No. 09/972,051, filed Oct. 9, 2001, now U.S. Pat. No.7,154,873, issued Dec. 26, 2006, which pursuant to 35 U.S.C. §119(a),claims the benefit of earlier filing date and right of priority toKorean Application Nos. 2000-59015, filed on Oct. 7, 2000, and2000-59016, filed on Oct. 7, 2000, the contents of which are herebyincorporated by reference herein in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a radio communication system and methodhaving a radio link control (RLC) layer. More specifically, theinvention relates to ciphering the payload data communicated by theradio communication system.

2. Background of the Related Art

Many efforts are being made to develop and study communicationtechnology admitting multimedia access without spatiotemporalimitations. Lately, the development of digital data processing andtransmission technology have enabled the realization of a real-timeglobal data communication system, using satellite, wireless, and wirecommunications. Access to information is freely available regardless ofwhether the information is voice, still image, or moving pictureinformation. IMT-2000 will be one of the communication technologiessupporting multimedia access.

An RLC layer is the second layer of a 3GPP protocol that controls datalinks and corresponds to the second layer of the 7-layered QSI model.RLC species used in 3GPP are mainly divided into a transparent (Tr) modespecie, to which no RLC header is added, and a non-transparent, (NTR)mode specie, to which an RLC header is added. NTr mode is subdividedinto an unacknowledged mode (UM), having no acknowledgment (ACK) signalfrom a receive stage, and an acknowledged mode (AM), having an ACKsignal from the receive stage. Therefore, RLC presently uses threemodes, designated as Tr, UM, and AM.

FIG. 1 illustrates a related art block diagram of an RLC AM entitystructure. On a transmitting side of the AM entity, segmentation andconcatenation are carried out through block 101 to change service dataunits (SDUs), stepping down from an upper layer, into uniformly sizedprotocol data units (PDUs). Headers containing sequence numbers (SNs)are added to the PDUs through block 102.

The PDU to which the header is added is transmitted to a multiplexer(MUX) 104 and stored in a retransmission buffer 103, for such later useas may arise. The PDU is conveyed by MUX 104 to ciphering block 105 toencrypt it fox data security. The encrypted PDU is temporarily stored ina transmission buffer 106, for later transmission to a field settingblock 107.

In the field setting block 107, fields such as a DC and poll field, butnot the sequence number of the RLC header, are set and then transmittedto a receive side AM entity. Such a PDU carrying data that has beenstepped down from an upper layer is called an AM data (AMD) PDU.

FIG. 2 illustrates a structure of an AMD PDU. The AMD PDU is constructedwith a header group, a length indicator (LI) group, a data field, and apadding (PAD) or piggybacked status PDU field.

The header group includes: (1) a sequence number field representing theorder of the respective AMP PDUs, (2) a 1-bit D/C field indicatingwhether the corresponding AMD PDU carries data information or controlinformation, (3) a 1-bit polling field (P field) to request a statusreport from a receiving side, (4) a 2-bit header extension (HE) fieldidentifying whether the next field is a data field or an LI field, and(5) a 1-bit extension (E) field identifying whether the next field is adata field or the LI field followed by an E bit field.

The LI octet contains an LI field and an E bit field, in which the LIfield identifies boundaries of the respective SDUs when the PDU includesa plurality of SDUs. Each LI octet represents an octet count from thefirst octet of the data part to the last octet of the respective SDUs.The respective LIs for the SDUs included in the PDU are called the LIgroup.

The data field includes at least one SDU stepped down from the upperlayer. Since the size of the data field is variable, padding is used tooctet-align the sizes of all the PDUs.

When ciphering is performed on the AMD PDU, the first two octets, whichare part of the header group, including the sequence number are notciphered. The rest of the AMD PDU is ciphered.

In the AM entity, both a control PDU and the AMD PDU exist. Varieties ofthe control PDU in dude a status PDU carrying status information, areset PDU resetting the AM entity, and a reset ACK PDU informing theacknowledgment (ACK) of the reset PDU.

FIG. 3 illustrates a structure of a status PDU. FIG. 4 illustrates astructure of a reset ACK PDU. The control PDUs, which are generated fromthe RLC control unit, are transmitted to the field setting block withoutundergoing the ciphering. The D/C and PDU type fields are set and thenthe control PDU is transmitted to the receiving RLC AM entity.

The D/C field is set to 1 for the AMD PDU and set to 0 for the controlPDU. When the AMD PDU is not completely filled with data, the remainingspace is padded. When there is a PAD in the AMD PDU, the field settingblock 107 enables the transmission of a status PDU instead of the PAD,so as to increase the data transmission efficiency. In this case, thestatus PDU is called a piggybacked status PDU. A demultiplex/routingpart 108 checks the D/C field. If the D/C field value is 0, the controlPDU is instantly sent upward to the RLC control unit 100, since a ‘0’identifies a control PDU. If the D/C field value is 1, the AMD PDU isinstantly sent upward to the receiver buffer 109, since a ‘1’ identifiesthe AMD PDU.

The RLC AM entity supports one or two logical channels for each radiobearer set-up. In FIG. 1, solid and dotted lines indicate the cases ofusing one or two logical channels, respectively. Data and controlchannels are differentiated when two logical channels are used.Therefore, the AMD PDU is immediately transmitted to the receiver buffer109 and the control PDU is transmitted to the RLC control unit 100, viathe demultiplex/routing part 108.

Receiver buffer 109 checks the receiving status of the respective AMDPDUs. If an AMD PDU is not received when expected, the receiver buffer109 sends a NACK signal to the transmitting side to request aretransmission of the missing AMD PDU. The received PDUs are stored inthe receiver buffer 109 until all of the PDUs forming a complete SDU arereceived. Thereafter, the receiver buffer 109 sends the PDUs to thedecipherer 110 as SDU units.

The PDUs are deciphered by a deciphering part 110 and data are extractedonly by removing RLC headers and piggybacked information from therespective PDUs, in block 111. Thus, the SDU is constructed with puredata through block 111. Subsequently, the SDU is sent upward to an upperlayer, though a reassembly part 112.

Unfortunately, the related art has problems in transmitting the AMD PDU.In order for the transmitting side to transmit the piggybacked statusPDU, the field setting block 107 checks whether a PAD exists. When a PADexists, the piggybacked status PDU replaces the PAD in the AMD PDU.Because the AMD PDU has been ciphered already, the ciphered AMD PDU hasto be deciphered in the field setting block 107 to determine the exactlocation of the PAD and whether the PAD exists. Moreover, the decipheredAMD PDU should be ciphered before transmitting the AMID PDU. Therefore,the deciphering/ciphering has to be cared out in the field setting blockunnecessarily.

The PDUs stored in the receiver buffer 109 have to be deciphered todetermines which PDUs belong to each SDU. Therefore, the receiver bufferalso needs to be able to decipher the PDU.

The repeated ciphering/deciphering reduces the processing speed andefficiency of the AMD PDU data and further degrades the systemperformance.

The RLC has an SDU discard function used for preventing the overflow ofa buffer. When this function is used, PDUs corresponding to the SDU arediscarded from both the transmitting buffer and the receiver buffer.Since all of the ciphered PDUs are stored in the transmitting andreceiver buffers, the transmitting and receiver buffers require thedeciphering function commonly.

FIG. 5 illustrates a construction of a related art RLC UM entity.Segmentation and concatenation are performed by block 122 to change theSDUs, stepping down from an upper layer through the UM-SAP, intouniformly sized PDUs. Subsequently, a ciphering part 123 ciphers thePDUs for data security. Then, an RLC header part 124 adds headerscontaining sequence numbers to the PDUs forming an unacknowledged modedata UMD PDU. A transmission buffer 125 stores and transmits the UMD PDUto a receiving side.

The UMD PDU is used when an ACK signal to the transmitting side from thereceiving side is not necessary. An AMD PDU is used when the ACK signalis necessary.

As shown in FIG. 6, the UMD PDU is constructed wit a header group, an LIgroup, a data field, and a PAD field. The header group includes asequence number field representing the order of the respective PDUs. Theheader group also has 1-bit extension (E) field indicating whether thenext field is the data field or the LI field followed by an extensionbit field.

The data field includes at least one SDU stepped down from the upperlayer. Since the size of the data field is variable, padding isperformed to octet-align the sizes of all the PDUs.

In the same manner as the AMD PDU, the LI group in the UMD PDU isconstructed with an LI field and an E bit field. The LI field identifiesthe boundaries of the respective SDUs, when the PDU includes a pluralityof SDUs. Each LI represents an octet count from the first octet of thedata field to the last octet of the respective SDUs. The respective LIsfor the SDUs included in the PDU are called the LI group.

The first octet is the header and is not ciphered. The rest of the UMDPDU is ciphered.

Referring again to FIG. 5, the RLC UM entity stores the transmitted UMDPDU in the receiver buffer 130. When all of the PDUs forming a completeSDU are received, the stored PDUs are transmitted to block 129 by therespective SDU units. Thereafter, the headers of the PDUs are removed inblock 129 and the PDUs are deciphered by a deciphering part 128. Thedeciphered PDUs are transmitted to an upper layer through a reassemblypart 127.

Unfortunately, the related art has problems in transmitting the UMD PDUusing the RLC UM entity. Because the PDUs are encrypted before beingconveyed to the receive-buffer 130, deciphering has to be performed bythe receiver buffer to determine which PDU belongs to which SDU.Therefore, the receiver buffer needs a deciphering function.

The RLC has an SDU discard function used for preventing the overflow ofa buffer. When this function is used, PDUs corresponding to the SDU arediscarded from both the transmitting and receiver buffers. Since all ofthe ciphered PDUs are stored in the transmitting and receiver buffers,the transmitting and receiver buffers require the deciphering functioncommonly.

SUMMARY OF THE INVENTION

Accordingly, the invention is intended to solve at least the aboveproblems and/or disadvantages and to provide at least the advantagesdescribed hereinafter.

An object of the present invention is to provide a radio communicationsystem having an RLC layer enabling the system to perform thetransmission and reception of PDUs more effectively.

Another object of the present invention is to provide a data processingmethod in a radio communication system having an RLC layer enabling thesystem to process PDUs faster in an RLC entity.

A data transmission module of a radio communication system having an RLCentity, according to the present invention, performs ciphering as afinal processing step after a transmission buffer. And, a data receivingmodule of a radio communication system having the RLC entity carries outdeciphering as a first processing step before a receiver buffer. An RLCentity according to the present invention includes an RLC AM entity andan RLC UM entity.

To achieve these objects and other advantages and in accordance with thepurpose of the invention, as embodied and broadly described herein, adata transmission module according to the present invention includes atransmission data storing module storing PDUs corresponding to SDUstransmitted from a first upper layer and outputting the stored PDUs bySDU unit, a ciphering module ciphering the PDUs stored in thetransmission data storing module and transmitting the ciphered PDUs to asecond RLC entity, a deciphering module deciphering ciphered PDUstransmitted from a first RLC entity, and a received data storing modulestoring the deciphered PDUs and outputting the PDUs toward a secondupper layer by SDU unit.

In another aspect of the present invention, in an RLC entity having atransmission buffer, a data processing method in the RLC entity includesstoring SDUs stepping down from a first upper layer in the transmissionbuffer in PDUs, ciphering the PDUs stored in the transmission buffer,and transmitting the ciphered PDUs to a second RLC entity correspondingto a receiving side.

In another aspect of the present invention, in an RLC entity having areceiver buffer, a data processing method in the RLC entity includesreceiving and deciphering PDUs received from a first RLC entitycorresponding to a transmitting side, storing the deciphered PDUs in thereceiver buffer, and reassembling the PDUs stored in the receiver bufferand then transmitting the reassembled data to a second upper layer.

Additional advantages, objects, and features of the invention will beset forth in part in the description which follows and in part willbecome apparent to those having ordinary skill in the art uponexamination of the following or may be learned from practice of theinvention. The objects and advantages of the invention may be realizedand attained as particularly pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in detail with reference to thefollowing drawings in which like reference numerals refer to likeelements wherein:

FIG. 1 illustrates a related art block diagram of a radio communicationsystem having an RLC AM entity;

FIG. 2 illustrates a structure of an AMD PDU;

FIG. 3 illustrates a structure of a status PDU;

FIG. 4 illustrates a structure of a reset ACK PDU;

FIG. 5 illustrates a related art construction of a radio communicationsystem having an RLC UM entity;

FIG. 6 illustrates a structure of a UMD PDU;

FIG. 7A illustrates a construction of a radio communication systemhaving an RLC AM entity, according to a first preferred embodiment ofthe present invention;

FIG. 7B illustrates the block diagram of FIG. 7A in greater detail;

FIG. 8A illustrates a construction of a radio communication systemhaving an RLC UM entity, according to a second preferred embodiment ofthe present invention;

FIG. 8B illustrates the block diagram of FIG. 8A in greater detail;

FIG. 8C illustrates a block diagram of another application of FIG. 8A;and

FIG. 8D illustrates the block diagram of FIG. 8C in greater detail.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings.

In a data transmission device of a radio communication system having anRLC layer, according to the main feature of the present invention, atransmission data reassembling module reassembles service data units(SDUs) received from an upper layer into protocol data units (PDUs). Aheader adding module then adds headers of the RLC layer to the PDUs.After that, a transmission data storing module stores the PDUs to whichthe headers are added. A ciphering module ciphers the PDUs to which theheaders are added and then transmits the ciphered PDUs to a lower layer.

In a data receiving device of a radio communication system having an RLClayer, according to the main feature of the present invention, adeciphering module deciphers ciphered PDUs of an RLC layer transmittedfrom a transmitting side through a lower layer. A received data storingmodule then stores the deciphered PDUs. An RLC header removing moduleremoves headers of the RLC layer from the PDUs. A reassembly modulereassembles the PDUs outputted from the RLC header removing module inservice data units (SDUs) and then transmits them to an upper layer.

FIG. 7A illustrates a construction of an RLC AM entity according to afirst preferred embodiment of the present invention and FIG. 7Billustrates the block diagram of FIG. 7A in greater detail. The RLC AMentity of the first preferred embodiment is mainly constructed with atransmission module 210, a receiving module 220, and an RLC controlmodule 230. Transmission module 210 is constructed with a first dataprocessing module 201, which converts SDUs transmitted from an upperlayer through AM-SAP 207 into PDUs; a transmission data storage module(or transmission buffer) 202 storing the AMD PDUs; and a cipheringmodule 203. Ciphering module 203 formats the PDUs stored in thetransmission buffer 202 into predetermined fields, under the control ofthe RLC control module 230, and ciphers the PDUs. The ciphered PDUs aretransmitted to an RLC AM entity corresponding to a receiving side,through channels DCCH and DTCH.

The receiving module 220 of the RLC AM entity is constructed with adeciphering module 204, which transmits control PDUs and deciphers AMDPDUs; a received data storage module (or receiver buffer) 205 thatstores the deciphered AMD PDUs; and a second data processing module 206.The second data processing module 206 reassembles the AMD PDUs stored inthe received data storage module 205 into SDU units and then transmitsthe AMD PDUs to the upper layer, through the AM-SAP 207.

Preferably, the transmission buffer 202 in the RLC AM entity processesthe data by SDU unit. Ciphering module 203 checks a D/C field before thePDUs are ciphered. The D/C field check distinguishes the AMD PDUs, whichare to be ciphered, from the control PDUs, which are not to be ciphered.If the AMD PDU includes a piggybacked status PDU, the piggybacked statusPDU is ciphered but the status PDU is transmitted without beingciphered. The receiver buffer 205 also processes the data by SDU unit.

FIG. 7B illustrates the block diagram of FIG. 7A in greater detail.Transmission module 210 of the RLC AM entity is constructed with asegmentation/concatenation module 211, which performs segmentation andconcatenation on SDUs stepped down from an upper layer; an RLC headermodule 212 forming PDUs by adding sequence numbers to the segmented andconcatenated SDUs; a retransmission buffer/management module 213 storingthe header-added PDUs for retransmission and management; a multiplexer(or multiplexing module) 214 outputting one of output signals of the RLCheader module 212 and the retransmission buffer/management module 213; atransmission buffer (or storage module) 215 storing the unciphered PDUsoutputted from the multiplexer 214; a set fields block (or set fieldsmodule) 216, which sets a D/C field and other fields in the PDU; and aciphering module 217, which ciphers the PDUs outputted from the setfields block 216 and transmits the ciphered PDUs to the receiving side.

Preferably, the ciphering module 217 checks the D/C field header of theAMD PDU before ciphering. Control PDUs are not ciphered, but the AMD PDUincluding any piggybacked status PDU is ciphered. Also, ciphering module217 checks the AMD PDUs for a PAD so that the PAD may be replaced by apiggybacked status PDU.

Receiving module 220 of the RLC AM entity is constructed with ademultiplexing/routing module 221, which transmits the control PDUsreceived from transmission module 210 of another entity to the RLCcontrol unit 230 and transmits AMD PDUs to a deciphering block 222; adeciphering module 222 that deciphers the AMD PDUs; a receiver buffer223 that stores the deciphered AMD PDUs and outputs the stored PDUs asSDU units; a header/piggybacked information removal module 224 thatremoves the RLC headers and piggybacked information from the PDUsreceived by the SDU unit; and a reassembly module 225 that reassemblesthe SDUs constructed with pure data and then transmits them to the upperlayer.

Preferably, the demultiplex/routing module 221 of the receiving module220 checks whether the transmitted PDUs are control PDUs or AMD PDUs,through an examination of the D/C field. Receiver buffer 223 transitsthe stored PDUs to the upper layer in the form of SDU units.

The first embodiment of the present invention introduces a new RLC AMentity that overcomes the ciphering/deciphering problems of the relatedart.

In the RLC AM entity structure, transmission module 210 performs theciphering step in a final stage, positioned after the set fields block.Receiving module 220 of the entity performs the deciphering step in aninitial stage positioned before the receiver buffer.

The steps of processing the AMD PDU in the RLC AM entity according tothe first embodiment of the present invention will now be explained indetail. One logical channel or two may be applied to the RLC AM entity.When two logical channels are applied, a UTRAN indicates that the firstlogical channel is used for data PDUs and the second logical channel isused for control PDUs.

If the instruction is not provided by the UTRAN, both the data andcontrol PDUs may be sent through one of the two channels and theidentification of the logical channel mapping is signaled by RRC.

SDUs stepped downward from the upper layers are segmented andconcatenated, through the segmentation/concatenation module 211, intoPDUs having fixed lengths. The length of the PDU is determined by theradio bearer reassembly and a semi-static value, which may be changedthrough the bearer reassembly by the RRC. Subsequently, the SDUs areconveyed to the RLC header module 212, where headers including sequencenumbers are added to the SDUs to form PDUs. The PDUs to which theheaders are added are immediately transmitted to the multiplexer 214 andsimultaneously stored in the retransmission buffer/management module213. For the purpose of concatenation and padding, the information bitsof the length indicator and extension are inserted into the initial partof the PDU.

Multiplexer 214 outputs PDUs from either the RLC header module 212 orthe retransmission buffer/management module 213. The multiplexer 214determines which PDUs are selected and when the PDUs will be transmittedto the MAC. The PDUs are provided the RLC PDU headers and PDU padding isreplaced by the piggybacked status information. PDUs transmitted throughthe multiplexer 214 are stored in the transmission buffer 215 in anunciphered state. From the transmission buffer 215, the PDUs aretransmitted to the set fields block 216. In the set fields block 216,the D/C field and other fields are set as necessary and the AMD PDU isreplaced by the piggybacked status PDU, if a PAD exists in the AMD PDU.

Ciphering module 217 ciphers the AMD PDUs outputted from the set fieldsblock 216 and transmits the ciphered AMD PDUs toward receiving RLC AMentity.

Before the ciphering is performed, the header D/C fields of the AMD PDUsare checked. In accordance with the value of the D/C field, ciphering isperformed on the AMD PDUs, including the piggybacked status PDU.Ciphering is not carried out on the control PDUs, such as the status,reset, and reset acknowledgment PDUs (reset ACK PDU).

When the piggybacked mechanism is applied, the padding is replaced bycontrol information so as to increase the transmission efficiency andenable faster message exchange between the peer entities. Thepiggybacked control information is not saved by a retransmission buffer.Piggybacked control information is included in the piggybacked statusPDU, which is subsequently included in the AMD PDU. The piggybackedstatus PDUs have variable sizes so as to be matched with an availableamount of free space in the AMD PDU.

Retransmission buffer 213 receives acknowledgment signals from thereceiving side, controls the retransmission of PDUs, and determines whena PDU is deleted from the retransmission buffer 213.

The receiving module receives the AMD PDUs through one of the logicalchannels, from the MAC sub-layer. The RLC PDUs are differentiated andpotential piggybacked status information is extracted. The PDUs arestored in the receiver buffer 205 until a complete SDU is received.Receiver buffer 205 may request a retransmission of a PDU by sendingnegative acknowledgment signal (NACK) to the peer entity.

Demultiplex/routing module 221 of the receiving module 220 judgeswhether the received PDUs are control PDUs or AMD PDUs, by examining theD/C field. The demultiplex/routing module 221 transmits the receivedPDUs, to the RLC control module 230, if they are control PDUs, or to thedeciphering module 222, if they are AMD PDUs.

Deciphered AMD PDUs are stored in the receiver buffer/retransmissionmanagement module 223. Receiver buffer/retransmission management module223 transmits the received PDUs to the upper module in the form of SDUunits.

The header and piggybacked information removal module 224 forms SDUs ofpure data, by removing the RLC headers and piggybacked information fromthe received PDUs. After the headers are removed from the PDUs and thePDUs are reassembled into one SDU, the SDUs are transmitted to the upperlayer. Reassembly module 225 reassembles the PDUs constructed with thepure data into the SDUs and then transmits the SDUs to the upper layerthrough the AM-SAP 207.

Meanwhile, the acknowledgment signals for the received PDUs are passedto the transmission module of the transmitting side.

As mentioned in the above description, the ciphering of PDUs isperformed in the final stage of the transmitting module and the PDUs aredeciphered in the initial stage of the receiving module. Therefore, thePDUs are stored in the transmission and receiver buffers in anunciphered state. Thus, the transmission and receiver buffers need nodeciphering function. Consequently, the PDU processing time in the RLClayers is reduced, since the transmission buffer, set fields block, andreceiver buffer require ciphering and deciphering capability.

Moreover, the piggybacked status PDUs are processed with ease in thepresent invention.

Since PDUs are stored in the receiver buffer in an unciphered state,other functions of the RLC may be performed directly on the SDU unit.Therefore, the data processing speed in the RLC is increased and the AMentity operates in a more stable manner.

Furthermore, the AMD PDUs, but not the control PDUs are ciphered,thereby reducing the processing time of the PDUs.

An RLC unacknowledged mode (UM) entity and its operation according to asecond embodiment of the present invention will not be explained. FIG.8A illustrates a construction of an RLC UM entity according to a secondembodiment of the present invention and FIG. 8B illustrates the blockdiagram of FIG. 8A in greater detail. The RLC UM entity shown in FIG. 9Aand FIG. 8B is characterized in that a transmitting module performs theciphering step after a transmission buffer and a receiving moduleperforms the deciphering step before a receiver buffer.

A transmitting module 310 of the RLC UM entity FIG. 8A is constructedwith a first data processing module 301, which converts SDUs steppeddown from an upper layer into transmittable PDUs; a transmission datastoring module (or transmission buffer) 302 storing the PDUs; and aciphering module 303 that ciphers the PDUs stored in the transmissiondata storing module 305 and transmits the ciphered PDUs to a receivingRLC UM entity.

A receiving module 320 of the RLC UM entity in FIG. 8A is constructedwith a deciphering module 304, which deciphers the PDUs transmitted fromthe transmitting RLC UM entity; a received data storing module (orreceiver buffer) 305 that stores the deciphered PDUs; and a second dataprocessing module 306 that transmits the PDUs stored in the receiveddata storing module 305 to the upper layer, through UM-SAP 307, in theform of SDU units.

Signal processing module 301 forms the SDUs stepped down from the upperlayer into PDUs and adds headers to the PDUs. The transmission buffer302 stores the UMD PDU and the ciphering module 303 ciphers the UMD PDUstored in the transmission buffer. The transmission buffer processesdata by the SDU unit. The ciphered UMD PDU is transmitted to thereceiving side of another UM entity through channels such as the CCCH,DCCH, DTCH, SHCCH, and CTCH. In this case, the RLC entity transfers theUMD PDUs to MAC through the channels. The channels CCCH and SHCCH areused for the UM only on a down-link. What channels are used depends onwhether the upper layer is located on a control plane or a user plane.

If the upper layer is located on the control plane, the channels CCCH,DCCH, and SHCCH are used. If the upper layer is located on the userplane, the channels CTCH and DTCH are used.

When the ciphered UMD PDU is received from the transmitting UM entitythrough one of the logical channels, the deciphering part 304 deciphersthe received UMD PDU and the receiver buffer 308 stores the decipheredUMD PDU.

An RLC header removing part 336 removes the RLC header from the UMD PDUstored in the receiver buffer 305. A reassembling part 338 reassemblesthe UMD PDU outputted from the RLC header removing part 309 into RLCSDUs and then transmits the reassembled UMD SDUs to the upper layerthrough the UM-SAP 307.

The receiver buffer 305 of the RLC UM entity processes data by the SDUunit also.

Referring now to FIG. 8B, the transmitting module 310 of the RLC AMentity is constructed with a segmentation/concatenation module 331,which performs segmentation and concatenation on the SDUs transmittedfrom the upper layer through the UM-SAP 307; an RLC header module 332,which forms PDUs by adding sequence numbers to the segmented data; atransmission data storing module (or transmission buffer) 333 thatstores the PDUs; and a ciphering module 334, which ciphers the PDUsstored in the transmission data storing module 333 and transmits them tothe receiving RLC UM entity. The segmentation/concatenation module 331and the RLC header module 332 in FIG. 8B are equivalent to the firstdata processing module 301 in FIG. 8A.

Receiving module 320 is constructed with a deciphering module 335, whichdeciphers the PDUs transmitted from the transmitting RLC UM entity; areceived data storing module (or receiver buffer) 337 that stores thedeciphered PDUs; an RLC header removing module 336 that removes the RLCheaders from the PDUs; and a reassembly module 338, which forms theSDUs. The SDUs are formed by reassembling the PDUs outputted from theRLC header removing module 337. After the SDUs are formed they aretransmitted to the upper layer through the UM-SAP 307. The RLC headerremoving module 336 and the reassembling module 338, in FIG. 8B, areequivalent to the second data processing module 306 in FIG. 8A.

The steps of transmitting and receiving the UMD PDU, in the RLC UMentity, according to the second embodiment of the present invention willnow be explained. The SDUs transmitted from the upper layer through theUM-SAP 307 are segmented and concatenated in thesegmentation/concatenation module 331 and then provided to the add RLCheader module 332. The add RLC header module 332 forms the PDUs byadding headers, including sequence numbers, to the segment data receivedfrom the segmentation/concatenation module 331. Transmission buffer 333stores the PDUs and then outputs them in the form of PDU units.Ciphering module 334 ciphers the PDUs stored in the transmission buffer333 and transmits the ciphered PDUs to the receiving side RLC UM entity.

The deciphering module 335 of the receiving side RLC UM entity deciphersthe PDUs transmitted through the channels. Receiver buffer 337 storesthe deciphered PDUs. Then, the receiver buffer 337 provides the PDUs, inthe form of SDU units, to the RLC header removing module 336, whichremoves the headers from the PDUs. The reassembling module 338 forms theSDUs, by reassembling the PDUs outputted from the RLC header removingmodule 336, and then transmits them to the upper layer.

FIG. 8C illustrates a block diagram of another application of the RLC UMentity. The order of the first data processing module 301 and thetransmission data storing module 302 are reversed from the order shownin FIG. 8A. The transmitting module 310 of the RLC UM entity includes areceived data storing module 302, which stores SDUs stepped down fromthe upper layer; a first data processing module 301, which converts theSDUs stored in the received data storing module into UMD PDUs; and aciphering module, which ciphers the UMD PDUs stored in the transmissiondata storing module 302 and then transmits them to the receiving RLC UMentity.

FIG. 8D is a detailed block diagram of FIG. 8C. The data transmissionmodule 310 includes a transmission data storage module 333 for storingservice data units from an upper layer, a segmentation and concatenationmodule 331 that acts as a transmission data reassembly module forreassembling protocol data units of the RLC layer, an RLC header module332 for adding headers of the RLC layer to the PDUs reassembled by thesegmentation and concatenation module 331, and a ciphering module 334that ciphers the header-added PDUs and transmits the ciphered PDUs to alower layer.

The construction of FIG. 8B is identical to that of 8D except that theserial ordering of the transmission data module 333 and the segmentationand concatenation module 331 are reversed. Therefore, the detaileddescription of 8D will be skipped. The construction of a receivingmodule 320 is equal to that of FIG. 8A of which an explanation may befound above.

Regarding FIG. 8C, as is the case in FIG. 8A, the SDUs are transmittedto the transmitting module through the UM-SAP 307 from the upper layer.Ciphered PDUs are transmitted toward the receiving RLC entity tough thechannels DTCH, DCCH, CCCH, SHCCH, and CTCH by the transmitting module.The ciphered PDUs enter the receiving module trough the channels DTCH,DCCH, CCCH, SHCCH, and CTCH and the PDUs outputted from the second dataprocessing module are transmitted to the upper layer through the UM-SAP.Also, the first data processing module includes asegmentation/concatenation module 331 carrying out segmentation andconcatenation on the SDUs transmitted from the upper layer, through theUM-SAP 307, and an RLC header module 332 forming PDUs by adding sequencenumbers to the segmented data.

In the RLC UM entity according to the second embodiment of the presentinvention, the ciphering and deciphering steps are arranged so that theunciphered SDUs are stored in the transmission buffer 333 and theunciphered PDUs are stored in the receiver buffer 336.

Since the transmission buffer 333 and the receiver buffer 336 storeunciphered data, they need no deciphering capability.

Accordingly, the RLC UM entity according to the second embodiment of thepresent invention has the following advantages. First, the cipheringstep is arranged as the final processing step in the transmitting moduleof the entity and the deciphering step is arranged as the initialprocessing step in the receiving module, thereby enabling the RLC entityto transit and receive PDUs more efficiently. Second, thealready-deciphered PDUs are stored in the receiver buffer, therebyenabling the receiving RLC entity to transmit UMD PDUs to the upperlayer more effectively and faster. Third, the transmission and receiverbuffers require no deciphering function, thereby enabling the RLC entityto reduce the data processing time spent on other RLC functions, such asthe SDU discard function.

The foregoing embodiments and advantages are merely exemplary and arenot to be construed as limiting the present invention. The presentteaching can be readily applied to other types of apparatuses. Thedescription of the present invention is intended to be illustrative, andnot to limit the scope of the claims. Many alternatives, modifications,and variations will be apparent to those skilled in the art. In theclaims, means-plus-function clauses are intended to cover the structuresdescribed herein as performing the recited function and not onlystructural equivalents but also equivalent structures.

1. A transmitting device having an acknowledged mode (AM) radio link control (RLC) entity in a mobile communication system, comprising: a segmentation and concatenation module that at least segments or concatenates service data units (SDUs) received from an upper layer; a header adding module that adds RLC headers to the at least segmented or concatenated SDUs for forming protocol data units (PDUs); a transmission storing module that stores the PDUs to which the RLC headers are added; a header field setting module that sets fields of the RLC headers in the PDUs received from the transmission storing module; and a ciphering module that ciphers the PDUs output from the header field setting module and then transmits the ciphered PDUs to a lower layer of the transmitting device, wherein the ciphering module checks D/C fields in the headers of the PDUs to determine whether the PDUs are data PDUs or control PDUs and ciphers the PDUs only if the PDUs are data PDUs, wherein the ciphering module ciphers piggybacked status PDUs in the data PDUs if the data PDUs include the piggybacked status PDUs.
 2. The transmitting device of claim 1, further comprising: a retransmission and management module that stores the header-added PDUs for retransmission and management; and a multiplexing module that multiplexes the PDUs output from the header adding module and the retransmission and management module.
 3. The transmitting device of claim 1, wherein the ciphered PDUs are transmitted to the lower layer through at least one of a plurality of channels for transmission, and the plurality of channels includes a dedicated traffic channel (DTCH) and a dedicated control channel (DCCH).
 4. The transmitting device of claim 1, wherein the SDUs are received from the upper layer through an acknowledged mode service access point (AM-SAP).
 5. A method of processing data at an acknowledged mode (AM) radio link control layer of a transmitting side in a communication system, the method comprising: at least segmenting or concatenating service data units (SDUs) received from an upper layer; adding RLC headers to the at least segmented or concatenated SDUs to form protocol data units (PDUs); storing the PDUs in a transmission buffer; setting fields in the RLC headers of the PDUs output from the transmission buffer; and ciphering the PDUs only if the PDUs are data PDUs, wherein whether the PDUs are data PDUs or control PDUs is checked using D/C fields of the RLC headers of the PDUs, wherein piggybacked status PDUs in the data PDUs are ciphered if the data PDUs include the piggybacked status PDUs.
 6. The method of claim 5, further comprising storing the RLC header-added PDUs for retransmission and management in a retransmission buffer.
 7. The method of claim 5, wherein ciphered PDUs are transmitted to a lower layer of the transmitting side through at least one of a plurality of channels for transmission, the plurality of channels includes a dedicated traffic channel (DTCH) and a dedicated control channel (DCCH).
 8. The method of claim 5, wherein the SDUs are received from an upper layer through an acknowledged mode service access point (AM-SAP). 